ms 660 problem,help required

[russ39]

ok people,heres a new issue to sort out.have a nice ms660 here that starts fine and goes very well for a short time anyway.revs and idles as it should when not under load but as soon as its placed on a log only cuts for approx 20 secs then dies away.thought carby problem so changed that for a good one and same issue is there.had a friend state it may be a coil issue.can anyone verify this or add a few maybe this scenarios,thanks

 

[Guido Salvage]

Fuel delivery issue.

 

[Tree Pig]

+1 on the fuel system. Sounds like maybe its sucking air and losing fuel flow. I would start with the cheapest and most common issue. Replace fuel line and filter.

 

[lentil]

+2 definitely fuel related. Hard to see that being a coil/spark issue.

 

[saxman]

Just thinking out loud here, tank vent? Before you go tearing everything down and possibly causing other issues. Take her back to the log and when it quits, open and close the fuel cap and let it get some air and see if that makes a difference. It could be pulling a vacumn in the tank due to a plugged vent. I think it is worth a try. Let us know.

Steve

 

[Johny Utah]

Here's what you do. First you pressure test and pull a vacuum on the carb and fuel pump. If that passes it's most likely your coil. They tend to run and when they get hot they die. As soon as it dies when hot do a spark test, if no spark it's your coil. You can double check your run circuit to see if that is the problem when hot too. You need to run a resistance check on your kill switch wires to the coil to look for a short or break in the wires. If you need more help PM me, I just took my master tech course for Stihl and we covered all this stuff. You should also pressure test and pull a vacuum on your fuel tank and tank vent to rule out a defective vent and possible cracked fuel line. If you really want to get fancy you can pressure test the crankcase too so you can detect leaking crank seals and a leaking impulse line. Good luck.:msp_smile:

 

[NORMZILLA44]

Had a saw just do this recently. It did just what you were saying O.P go good a short time, and quit. Had me stumped a day or two, because my other fuel line issues in the past were cut and dry. They would just bog out and quit. Found out this one saw had a hole in the line up higher, so it went awhile then the fuel level dropped then air was sucked in.

 

[russ39]

you guys are awesome

Had a saw just do this recently. It did just what you were saying O.P go good a short time, and quit. Had me stumped a day or two, because my other fuel line issues in the past were cut and dry. They would just bog out and quit. Found out this one saw had a hole in the line up higher, so it went awhile then the fuel level dropped then air was sucked in.

thanks ever so much for all your input,two faults found breather was blocked and not functioning and the fuel line had a small split just below the elbow and wasnt getting the gas through.......help appreciated regards russell
:msp_thumbup: